4.236 & T4.236 DIESEL ENGINES Section T: Turbocharger Caterpillar

Section T: Turbocharger
1.1. T4.236 Engines only
2.1. Wastegate Turbocharger
3.1. Maintenance
4.1. To Remove Turbocharger
5.1. Airesearch T-31 (see Fig. T.3)
6.2. Dismantling
7.2. Cleaning
8.2. Internal Parts Inspection (see Fig. T.4)
9.2. Re-assembly
10.2. To Fit Turbocharger
11.2. Wastegate Operation/Calibration Test

T4.236 Engines only

The turbocharger is fitted on the exhaust manifold outlet, see Fig. A.2. It is lubricated by oil taken from the engine lubricating system. Oil pressure should never drop below 30 lbf/in2 (2,11 kgf/cm2) or 207 kN/m2 at normal running speed. Check this pressure regularly.

The maximum boost pressure should be 11-13.5 lbf/in2 (0,80-0,95 kgf/cm2) or 76-93 kN/m2 when the engine is running at maximum speed and full load.

With some engines where it is not possible to fully load the engine, the boost pressure will be somewhat lower.

No attention need be paid to the speed of the turbocharger since this varies automatically with the speed and load of the engine.

Wastegate Turbocharger

On some engines a 'Wastegate' turbocharger is fitted. This is different from the standard turbocharger in that a wastegate unit fits in the turbine housing inlet passage and controls the amount of exhaust gas reaching the turbine. This controls shaft speed and compressor output pressure. The position of the wastegate control valve is determined by a differential-pressure sensing diaphragm which automatically keeps the boost pressure from exceeding 11 lbf/in2 (0,80 kgf/cm2) 76.0 kN/m2, at all engine speeds.


Every 20,000 miles (30,000 km) or 1,000 hours, clean the oil drain pipe from turbocharger to sump, also turbocharger compressor wheel and cover.


Remove the air inlet duct and compressor housing and check for dirt or dust build-up (see Fig. T.1).

Remove all foreign matter - determine and correct cause of build up.

Use soft brush on compressor wheel as uneven deposits can affect rotor balance and cause bearing failure.

With the compressor housing removed, push the compressor wheel towards the turbine wheel and turn rotating assembly by hand: check for binding and rubbing. Listen carefully for unusual noises. If binding or rubbing is evident, remove the turbocharger for dismantling and inspection.

To Remove Turbocharger

Disconnect turbocharger inlet and outlet connections.

Disconnect exhaust pipe.

Remove oil supply pipe and release oil drain pipe.

Release turbocharger outlet assembly from the cylinder block.


Remove turbocharger from exhaust manifold, (see Fig. T.2).

Seal open engine connections.

Airesearch T-31 (see Fig. T.3)



Clean the exterior with a pressure spray of a non-caustic cleaning solvent before dismantling. Dismantle only as required to make necessary inspection or repairs. Note: The 'Wastegate' unit where fitted, cannot be dismantled. See page T.4 for service/calibration instructions. As each part is removed, place in a clean container to prevent loss or damage.

Remove the bolts, clamps and lockplates which hold the compressor and turbine housings to the centre housing group. Tap the housings with a soft faced hammer if force is needed for removal.

NOTE: Exercise caution when removing housings to prevent damage to compressor or turbine wheel. Once damaged, they cannot be repaired. Never attempt to straighten bent compressor or turbine blades-replace the faulty component.

Place the centre housing group in a suitable holding fixture which will prevent the turbine wheel from turning.

Use a T-handled wrench when removing the compressor wheel locknut to avoid possible bending of the shaft.

Lift the compressor wheel off the shaft. Remove the shaft wheel from the centre housing keeping shaft central with bearings until clear of centre housing.

NOTE: The turbine wheel shroud is not retained to the centre housing and will fall free when the shaft wheel is removed.

Remove lockplates and bolts from back plate.

Tap backplate with soft mallet to remove from recess in centre housing.

Remove thrust collar and thrust bearing from centre housing.

Remove bearings and retainers from centre housing. Discard rubber sealing ring.


Before cleaning, inspect all parts for signs of rubbing, burning or other damage which might not be evident after cleaning.

Soak all parts in clean non-caustic carbon solvent. After soaking, use a stiff bristle brush and remove all dirt particles. Dry parts thoroughly.

NOTE: Normally a light accumulation of carbon deposits will not affect turbine operation.

Internal Parts Inspection (see Fig. T.4)


Parts must now show signs of damage, corrosion or deterioration. Threads must not be nicked, crossed or stripped.

The turbine wheel must show no signs of rubbing and vanes must not be torn or worn to a feather edge. The shaft must show little signs of scoring, scratches or seizure with the bearings.

The compressor must show no signs of rubbing or damage from foreign matter. The compressor wheel bore must not be chafed.

Seal parts must show no signs of rubbing or scoring of the running faces. Housings must show no signs of contact with rotating parts. Oil and air passages must be clean and free from obstructions.

Burnish or polish out minor surface damage. Use silicon carbide abrasive cloth for aluminium parts and crocus abrasive cloth for the steel parts. Thoroughly clean parts before re-assembly.

Replace any parts which do not meet requirements.

Replace the following parts: seal ring, lockplates, piston rings, turbine housing bolts, journal bearings, bearing retaining rings and compressor wheel locknut. If thrust bearing and thrust collar show signs of nicks, scores, varnish deposits or foreign matter embedments-replace. Also, a close inspection of bearing bores in the centre housing should be made and if any of the above conditions exist, replace the centre housing.


Check each part prior to installation to ensure cleanliness. Exercise care to prevent entry of foreign matter during assembly.

Check thrust collar piston ring groove for nicks or burns.

Assemble in the following manner:

Install inboard bearing retainers. Lubricate bearings with clean engine oil. Fit bearings and outer bearings retainers.

Place turbine wheel upright. Gently guide shaft through shroud and centre housing bearings. Place thrust bearing over thrust collar.

Fit piston ring on thrust collar. Place thrust collar over shaft so that thrust bearing is flat against the centre housing and engages the centre housing anti-rotating pins.

Install seal ring in groove in centre housing.

Ensure that thrust spring is installed in back plate. Align mounting holes of centre housing and backplate and install over shaft and thrust collar. Use care not to break piston ring when engaging seal into back plate bore. Back plate is easily installed if open end position is engaged into back plate bore first.

Install compressor backplate, bolts and lockplate Tighten to 79 lbf in (104 kgf cm) or 8,93 Nm and secure lockplates.

Fit compressor wheel. The larger face of the locknut and the front face of the impeller must be smooth and clean. Lightly oil threads and face of nut and tighten to 20 lbf in (23 kgf cm) or 2,26 Nm. Then continue to tighten until length of shaft increases by 0.0055/0.0065 in (0,14/0,16 mm). Tighten nut by using T-handled wrench to avoid side load which may cause shaft to bend. Check axial end play for 0.001/0.004 in (0,03/0,10 mm) travel. If equipment is not available to measure shaft stretch, this alternative method may be used: after installing impeller nut and tightening to 20 lbf in (23 kgf cm) or 2,26 Nm continue to tighten through an angle of 110°.

Check for clearance between wheel shroud and turbine wheel.

Orientate compressor housing to centre housing. Fit the six bolts and three lockplates. Tighten bolts to 130 lbf in (150 kgf cm) or 14,09 Nm.

Orientate turbine housing to centre housing. Coat bolt heads with a high temperature thread lubricant Install bolts, clamps and lockplates. Tighten bolts to 130 lbf in (150 kgf cm) or 14,09 Nm. Bend up lockplates.

After assembly, push the rotating assembly as far as possible from the turbine end and check for binding. Repeat check, pushing from compressor end. If the unit is to be stored, lubricate internally and install protective covers on all openings.

NOTE: The turbocharger does not require testing after overhaul.

To Fit Turbocharger

Remove seals from open engine connections.

Fit turbocharger to exhaust manifold, use a new gasket.

Fit turbocharger outlet assembly to cylinder block.

Fit oil drain pipe, use a new gasket.

Pour 4 to 5 (fluid ounces (110/114 ml) of clean engine oil through oil inlet port of turbocharger central housing. Turn rotation assembly by hand to pass oil over bearing surfaces.

Connect compressor inlet and outlet pipes and exhaust pipe.

Fit oil supply pipe but do not tighten setscrews.

Operate the stop control and turn engine by the starter motor until a steady flow of oil comes from the oil supply pipe.

Tighten pipe flange setscrews.

Start the engine and check for leaks. The engine must be run at idling speed for three to four minutes to allow the lubricating oil to flow before the engine speed is increased.

Wastegate Operation/Calibration Test


Remove turbocharger from engine and the hose from the wastegate unit sensing port. (see Fig. T.5).

Attach a dial gauge to the turbocharger so that the dial indicator rests on the control valve face. (see Fig. T.5).

Set the indicator dial to zero and while gently tapping the turbine housing with a soft mallet apply calibration air pressure of 10.8 - 11.8 lbf/in2 (0,76 - 0,86 kgf cm2) 74,5 - 81,4 kN/m2 to the wastegate sensing port. (Note, the wastegate is designed to allow a small bleed-off of pressure).

Ensure the specified pressure is maintained at the sensing port during this test.

Note the valve movement shown on the indicator dial.

Release the air pressure at the wastegate unit sensing port and ensure the dial indicator pointer returns exactly to zero.

Repeat steps 3 to 6 several times to make sure that the wastegate unit valve movement has been accurately measured.

If a valve movement of 0.050 in (1,27 mm) cannot be obtained within the specified pressure range, the turbine housing complete with wastegate unit, will have to be renewed.

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